A couple of tricks that Travis and I talked about over the years on the IDI valve covers.....
1. Every time you remove the torque spreaders, flip them over when you put the, back on. The spreaders do get a bit deformed each time they are torqued. When you flip them the torque helps to flatten them back out.....
2. If you do not have an inch-pound 1/4 drive torque wrench, tighten them with a nut driver. With a nut driver, you can't put as much torque as with a wrench/ratchet. There just isn't as much leverage available. Also, with the nut driver, they just need to be snug, don't double hand and twist with all ya got..... Remember, the early 6.9's had Phillips head screws, not hex head bolts.... Many years ago he bought a 1/4 drive inch-pound torque wrench specifically for the valve covers.....